1. Field of the Invention
The invention relates to optical fiber technology and, more particularly, to a device for storing and deploying optical fiber cable in a manner that enables continuous adjustment to the length of optical fiber cable that may be stored and/or deployed.
2. Description of the Related Art
Largely because of the demonstrated capacity to transport prodigious quantities of data, optical fiber cable finds extensive application in telephony, computer systems and other applications where large quantities of data or information must be conveyed. However, unlike metallic conductors, optical fibers are brittle and may fracture if bent beyond a minimum bend radius. Even at bending radii greater than that at which cracking or breaking may occur, performance of the optical cable may nonetheless be degraded as a result of optical loss within the fibers that are subjected to the bending. For example, although the bend radius that may cause cleavage of fiber optic cables used in telecommunications applications may be approximately 12 mm, degradation in performance may occur at larger radii, starting at a bend radius of approximately 25 mm. In the discussion to follow, the bend radius at which degradation in optical performance becomes noticeable will sometimes be referred to as the “minimum bend radius”.
Further, since a cable may be covered or enclosed in a sheath, or since only selected fibers in a cable may break, a break may not be detected until there has been loss of data. At that point, the break may then be inconvenient to localize and may be both difficult as well as expensive to correct. It is, therefore, desirable that when such cables are handled, suitable constraints be observed so as to assure that the cable is not bent at a radius that violates an applicable minimum bend radius restriction.
A common situs for a break or other degradation in a fiber optic cable as a result of overbending may be found at switching panels in a telephone carrier's central office. Typically, a large number of interconnect switching or other types of circuits are mounted adjacent each other in a panel, with cables extending from a selected side or sides of each of the circuits. In one application, there may be multiple cables, each extending from each circuit. Some of the cables may represent inputs and others outputs for the circuit, and it is desirable that cables exiting a given circuit be able to extend toward either end of the panel to interconnect with other circuits on the panel or with circuits and locations external to the panel. However, to avoid undesirable signal degradation or discontinuities occurring in the cables, it is important that in extending the cables from the circuit board through the panel the cables not be excessively stressed at any point along the path of travel. Existing systems for managing and controlling the distribution of fiber optic cables in a switching panel generally do not provide specific guides that assure that cables are not overbent as they are run through the panel, while concurrently accommodating multiple cables and permitting multiple routing directions. Similar problems, also unresolved, may also be germane to other transmission media, such as coaxial cable systems, where characteristic impedance may be altered or where wire or shielding may be cracked or broken if excessive bending occurs.
Typical existing devices permit optical fiber cable to be wound only around a fixed radius. This radius is usually 27 mm or greater, so as to minimize signal loss due to the bending of the fiber. These devices tolerate only discrete incremental take-up adjustments, roughly concomitant to the perimeter of the geometry around which the fiber is wound. Some devices incorporate multiple paths to afford at least a limited adjustment of the take-up length. In order to route a length of optical fiber cable from source to destination often requires exceeding the minimum bend radius, and sometimes stresses the cable beyond physical limits. In addition, many known devices incorporate multiple capture tabs to contain the fiber within the defined paths. The capture tabs are necessary in most systems, but repetitive use required by trial and error causes fatigue and breakage in the cable and in the tabs themselves.
Accordingly, what is desired is a device that promotes convenient protection, storage deployment of optical fiber cable. The device will accommodate the accumulation of a generous length of cable so that sufficient cable is on hand to satisfy a continual need to make and modify connections to and between telecommunications equipments with interconnection panels, such as optical switches, multiplexers, digital cross-connects and the like. Preferably, the device will facilitate continuous adjustment in the length of cable that is stored and/or deployed, thereby responding to the myriad configurations encountered in the length of cable distributed by cable suppliers, manufacturer equipments and carrier installation environments. Repeated requirements to add or remove cable from the device are to be minimized, if not eliminated. The device provides a space for the fibers to accumulate in a controlled manner, always observing the minimum bend radius. That is, the device allows lengths of cable to be added to or withdrawn from the space to conform to installation requirement. The designer can define a path from source to destination with the proper bend radius, confident that the device will prevent over bending. Manufacturing tolerances may then be relaxed to provide economy without sacrificing optimal performance.